This invention relates to fire protection sprinkler arrangements and, more particularly, to sprinkler arrangements utilizing very extra large orifice sprinklers, which are capable of operating at relatively low water pressure to provide protection for certain special occupancy hazards as described herein.
For many years, the National Fire Protection Association (NFPA) has promulgated and maintained standards which are relied upon by local authorities in approving the design of proposed fire protection systems. Among those standards are the Flammable and Combustible Liquids Code NFPA 30, the Manufacture and Storage of Aerosol Products Code NFPA 30B, the General Storage Standard NFPA 231, which relates to the storage of many commodities including Class I, Class II, Class III and Class IV commodities representing a broad range of materials including Group A, Group B and Group C plastics that are stored palletized or stored in slatted wooden crates, solid wooden boxes, multi-wall corrugated cartons or equivalent combustible packaging materials or wooden pallets, Rack Storage Standard NFPA 231C which relates to protection of a broad range of commodities including plastics stored in racks, Rubber Tire Storage Standard NFPA 231D, which relates to indoor storage of rubber tires, Roll Paper Storage Standard NFPA 231F which relates to storage of roll paper, and the protection of Records Standard NFPA 232. As used herein, the commodities and storage conditions described in those standards are called "special occupancy hazards".
Because of the difficulty in protecting special occupancy hazards of the type described in the above cited NFPA standards, each of those standards has heretofore specified a minimum design water pressure of 10 psi (0.7 bar) and has required the use of sprinklers having a maximum orifice diameter of 5/8 inch (15.9 mm.) for sprinkler systems designed to protect such hazards. In some cases these requirements apply to storage height exceeding 12 feet.
Such sprinklers have a nominal K factor of 11, where the K factor represents the rate of water flow through the sprinkler in gallons per minute divided by the square root of the water pressure applied to the sprinkler in pounds per square inch. In this regard, it is desirable to provide sprinkler arrangements for such special occupancy hazard having a higher K factor since lower pressures can then be utilized.
It has been universally believed and accepted throughout the industry, however, that lower design pressures, below 10 psi (0.7 bar), or larger sprinkler orifices (higher K factor) could not provide adequate protection for special occupancy hazards of the type to which those standards are directed. In many instances, such sprinkler size and system pressure requirements impose undue limitations on the design and construction of fire prevention sprinkler systems and result in increased construction costs.